1. Field of the Invention
The present invention relates to seismic systems in general and, more particularly, to signal to noise determination for seismic systems.
2. Description of the Prior Art
One of the most important steps in the inspection of a digital field recording system is the determination of its signal to noise ratio. Heretofore the best aid in the determination of the signal to noise ratio involved the use of a centrally located general purpose computer. A record is recorded on digital tape by the recording system noise at minimum system gain. The minimum gain word is then submitted to the computer where the five most positive digital numbers and the five most negative digital numbers of each tape channel are printed on a computer paper print out. To determine the signal to noise ratio, the difference between the most positive and the most negative digital numbers must be taken for each channel. This difference is compared to values in a reference table. The signal to noise ratio is then determined from the table. The biggest disadvantage to this aid is the computer turn around time. If the system to be inspected is tested at the computer processing center it will take one to two days to determine the signal to noise ratio. If the system is in the field, the records must be brought back to the computer center and a minimum of three of four days is needed to determine the signal to noise ratio.
Another aid is called a noise decoder. The noise decoder must be used with an oscilloscope. The output of the noise decoder is not the signal to noise ratio but converter bits from which an approximate signal to noise ratio can be derived. The main disadvantage is that the exact signal to noise ratio cannot be found easily if at all. The reason for this is that the output of the noise decoder displays all changes serially across the oscilloscope screen without capturing the most positive or most negative words. It is possible that a noise spike can occur that the scope observer can miss with his eye.
The present invention provides for on-site signal to noise ratio determination for each channel in a seismic system.